Abstract
In this study, a novel quantum mechanics-based protocol for the evaluation of carcinogen-scavenging activity (QM-CSA) is developed. The QM-CSA protocol represents a universal and quantitative approach to evaluate and compare the activation-free energies for alkylation reactions between individual polyphenolic compounds and chemical carcinogens of the epoxy type at physiological conditions by applying two scales: the absolute scale allowing for the comparison with guanine and the relative scale allowing the comparison with glutathione as a reference compound. The devised quantum mechanical methodology was validated by comparing the activation-free energies calculated with 14 DFT functionals in conjunction with two implicit solvation models (SMD and CPCM) and the experimental activation-free energies for reactions between nine investigated chemical carcinogens and guanine. According to the obtained results, the best agreement with experimental data was achieved by applying DFT functionals M11-L and MN12-L in conjunction with the flexible 6-311++G(d,p) basis set and implicit solvation model SMD, and the obtained uncertainties were proven to be similar to the experimental ones. To demonstrate the applicability of the QM-CSA protocol, functionals M11-L, and MN12-L in conjunction with the SMD implicit solvation model were applied to calculate activation-free energies for the reactions of nine investigated chemical carcinogens of the epoxy type with three catechins, namely EGCG, EGC, and (+)-catechin. The order of CSA in this series of catechins in comparison to guanine and glutathione was determined as (+)-catechin > EGC > EGCG. The obtained results, for the first time, demonstrated the evaluation and comparison of CSA in a series of selected catechins with respect to glutathione and guanine. Moreover, the presented results provide valuable insights into the reaction mechanisms and configurations of the corresponding transition states. The novel QM-CSA protocol is also expected to expand the kinetic data for alkylation reactions between various polyphenolic compounds and chemical carcinogens of the epoxy type, which is currently lacking in the scientific literature.